1. Field of the Invention
The present invention relates to an ultrasonic probe to be furnished on an ultrasonic diagnostic apparatus.
2. Description of the Related Art
The ultrasonic diagnostic apparatuses are broadly used in the medical field, which are to examine a subject by sending an ultrasonic wave into the subject and receiving a reflection wave, an echo signal, from the subject. The ultrasonic diagnostic apparatus is furnished with an ultrasonic probe for transmitting and receiving an ultrasonic wave. The ultrasonic probe is to be used by an abutment against the examination subject.
The ultrasonic probe structure in the conventional art is explained. As shown in FIG. 11, a probe proper 102 has a probe housing 103. The probe housing 103 accommodates therein a transducer unit 128, a flexible printed-wiring board 108, and a magnetic-shield member 112. The transducer unit 128 is made up with a transducer 104, an acoustic matching layer 105, an acoustic lens 106 and a backing material 107. The transducer 104 has a plurality of transducer elements arranged in one-dimensional or two-dimensional form. The transducer element is made up by a piezoelectric element that is typically a vibrator, a common electrode formed on one surface of the piezoelectric element and a discrete electrode formed on the opposite surface. A plurality of discrete electrodes provided to the plurality of transducer elements are extended by a plurality of signal lines printed on the flexible printed-wiring board 108. The plurality of signal lines are connected to a plurality of cable wires 111. The plurality of cable wires 111 in a bundle constitute a cable 109, cooperatively with a coating of plastic, etc. The cable 109 is extended out of the probe housing 103 through a clamp 110. The probe proper 102 is connected to an external ultrasonic diagnostic apparatus by the connector 101 provided at an end of the cable 109.
The transducer 104 generates heat during the conversion of ultrasonic wave/electricity. The ultrasonic wave generated by the transducer 104 is partly absorbed in the transducer 104. This causes heat. Meanwhile, the flexible printed-wiring board 108 is mounted with an electronic circuit, such as a multiplexer. Heat is generated on the electronic circuit.
The ultrasonic probe is to be put on the surface of a subject. For this reason, the acoustic lens 106, for contact with a subject, has a surface temperature whose upper limit value is set up. Meanwhile, the image S/N obtained in the ultrasonic diagnostic apparatus improves in proportion to the increase of ultrasonic-wave transmission power. Consequently, there is a need to raise the ultrasonic-wave transmission power in a range the surface temperature of the acoustic lens 106 does not reach its upper limit value.
In the conventional countermeasure against heat, there are included a provision of means of transferring the heat, generated at a transducer, to a point distance from the transducer (JP-A-9-140706), a provision of means of conducting the heat, generated at a transducer, to a cable (JP-A-10-94540), and a provision of two kinds of sealing resins (JP-A-10-85219).
However, the drive scheme/condition to send and receive an ultrasonic wave by the ultrasonic diagnostic apparatus is not limited to one but diagnosis is conducted by changing the drive scheme/condition in accordance with diagnostic content from time to time. Accordingly, the heat generated in an ultrasonic probe actually is different in amount depending upon driving scheme/condition.
Meanwhile, there is a need to set a use condition of the ultrasonic probe by assuming a drive scheme/condition and use way to raise temperature the greatest so that temperature can be maintained for safety even under such conditions. Consequently, in a certain case, temperature rise is less under a certain drive scheme/condition wherein there is provided a margin to a safety criterion. Meanwhile, in another drive scheme/condition, temperature rise be significant so that the ultrasonic diagnostic apparatus is used in a situation on a side closer to a safety criterion. In this manner, there is a great difference in safety depending upon drive scheme/condition.
In a certain drive scheme, ultrasonic-probe transmission acoustic power and circuit-board consumption power are suppressed in order to maintain the temperature for safety, thus sacrificing the image quality obtained.
It can be considered to provide a structure the temperature is not ready to change by providing a great specific heat in average to the ultrasonic probe, as an approach to suppress against the temperature rise while taking account of the difference in ultrasonic-probe temperature rise due to the difference in drive scheme/condition. Meanwhile, those light in specific gravity are preferred in order to enhance the operationality of the ultrasonic probe. However, the use of a material having a great specific heat generally requires a greater specific gravity, thus leading to the weight increase in the ultrasonic probe entirety. This increases the burden on the operator who manipulates the ultrasonic probe. It is the general tendency that specific weight increases with increase in specific heat. This makes it impossible to expect a material meeting the both properties.